秦岭洛南-栾川断裂带角闪石的变质变形特征及其意义

Deformation and metamorphic characteristics of amphiboles in the Luonan-Luanchuan fault belt of the Qinling Orogen and its significance

断裂带基性构造岩中的角闪石变形行为及变形过程中成分变化是研究断裂带变形环境及构造演化的重要手段,也是研究中地壳角闪质岩石流变学特征的重要依据。本文通过对洛南-栾川断裂带庙子构造剖面中基性糜棱岩和构造片岩中角闪石的变质变形分析研究表明角闪石的显微变形特征以膨凸式和亚颗粒式动态重结晶为主,其变形环境应为角闪岩相。探针成分分析显示角闪石全部为阳起石,具有明显的成分环带,角闪石Al2O3-Ti O2图解显示其核部成分偏壳幔混合,边部成分偏壳源;（Na＋K）-Ti变异图显示其形成环境主要为角闪岩相,核部偏麻粒岩相,边部偏绿片岩相。与角闪石共生斜长石也具有明显的成分环带,残斑核部成分偏基性,边部及基质中新生斜长石成分偏酸性。用斜长石-角闪石实验地质温压计计算结果指示了核部温压为620～640℃,0.4～0.7GPa;幔部的温压为490～520℃,0.15～0.65GPa;边部的温压为465～482℃;0.5～0.8GPa。所以,庙子基性糜棱岩中角闪石的核部形成于相对较高温的深部环境;边部是在断裂带剪切作用下,产生塑性变形和退变质偏壳源成分的环带,反映出在活动过程中有一定的抬升。所以,由断裂带角闪石的变质变形分析可以揭示断裂带的构造活动过程以及温压环境,对研究造山带中断裂带的活动条件及演化有重要意义。

The deformation behavior and the component variation of amphiboles in the meta-mafic rocks in the fault belt are important means to study deformation environment and tectonic evolution of the fault belt. They also provide important information for study the rheological characteristics of amphibolites in mid-crust. With deformation and metamorphic analysis of amphiboles in the basic mylonite and the tectonic schist from Miaozi structural section of the Luonan-Luanchuan fault belt,it is suggested that the amphibole mainly deformed as BLG and SR,and the deformation environment should be amphibolite facies. Microprobe analysis indicated that all of the amphiboles are actinolite with significant compositional zoning. Al2O3-Ti O2 graphic of amphibole shows its component most like to be mantle-crust mixing origin in the core and crust-source in the edge.（ Na ＋ K）-Ti variogram shows the formation environment of the amphibole is mainly amphibolite facies,and granulite facies in the core,greenschist facies in the edge. The feldspar intergrowth with amphibole also has significant compositional zoning,which are basic in the core and acidic in the edge and matrix. With feldsparamphibole experimental geothermobarometry,we figured up the temperature and pressure are respectively 620 ～ 640℃ and 0. 4 ～0. 7GPa in the core,490 ～ 520℃ and 0. 15 ～ 0. 65 GPa in the mantle,and 465 ～ 482℃ and 0. 5 ～ 0. 8GPa in the edge. In conclusion,the core of amphibole in the basic mylonite from Miaozi profile was formed in comparatively deep environment with higher temperature and the edge with crust-source compositional zoning was formed in the process of ductile deformation and retrograde metamorphism during shearing of the fault belt,which indicates the uplift during tectonic activities. So,metamorphic and deformation analysis of amphibole from fault belt can help reveal the tectonic activity process and the temperature-pressure environment,which has important significance to study the forming environment and evolution of fault belts in orogenic belt.